Case 3: Diabetes – Point-of-Care Blood Glucose Monitoring (Endocrine and Immunity, PY512)

Flashcards covering the principles, devices, error sources, HbA1c, and detection methods related to point-of-care diabetes diagnostics.

What is the working principle of a finger-prick blood glucose test strip?

An electrochemical biosensor using glucose oxidase and a mediator; glucose oxidation generates an electrical current proportional to glucose concentration.

Which enzyme is used in glucose finger-prick test strips?

Glucose oxidase.

What is the role of the mediator in GOx-based test strips?

Transfers electrons from the reduced enzyme to the electrode, enabling current generation.

What product is formed when glucose is oxidized by glucose oxidase in these strips?

Gluconolactone (with hydrogen peroxide as a byproduct; mediator handles electrons).

What are the main types of glucose monitoring devices mentioned in the notes?

Finger-prick test strips, continuous glucose monitors (CGM), and flash glucose monitors.

Where does CGM measure glucose?

In the interstitial fluid surrounding cells under the skin, not directly in blood.

What are the main components of a CGM system as shown?

A skin-mounted glucose sensor and a transmitter that sends data to a reader/monitor.

What is HbA1c and what does it reflect?

Glycated haemoglobin; reflects average blood glucose over the past 2–3 months.

HbA1c assay principle described in the notes?

Two reactions: measurement of Hb, and measurement of HbA1c using fructosyl peptides with fructosyl peptide oxidase and peroxidase for color development.

What accuracy standards do ISO and FDA require for glucose measurement results?

At least 95% of results must be within ±1.11 mmol/L for readings

What are the four main categories of error sources in glucose testing?

Instrumental/operational errors, environmental errors, physiologic interactions, and chemical/biological agents.

Give examples of factors causing inaccuracy in CGM readings (from notes).

Calibration issues, selectivity problems, biofouling, enzyme degradation, temperature effects, and vitamin C supplements (noted for flash monitors).

Name drug interferences listed for CGM devices.

Paracetamol/acetaminophen, hydroxyurea, and ascorbic acid (vitamin C).

What is the key difference between continuous glucose monitoring and flash glucose monitoring?

CGM provides continuous data and trends; flash monitoring requires scanning with a reader to retrieve readings.

What is the advantage of CGM/flash devices in terms of data?

They allow tracking glucose trends over time, not just a single snapshot.

What are the general detection mechanism categories for glucose monitoring devices?

Electrochemical (E), Optical (O), and Combinatorial/Other (C) detection mechanisms.

How is HbA1c formed at the molecular level (briefly)?

Non-enzymatic glycation of hemoglobin via Schiff base formation, followed by rearrangement to an Amadori product.

What is HbA1c measuring in terms of time period?

Average blood glucose over the past two to three months.

What basic components are embedded in a glucose test strip's reagent system?

Base substrate with reagent system including glucose oxidase, mediator, and electrode contacts.

Where does the interstitial fluid glucose measurement occur in CGM?

In the interstitial fluid surrounding tissue cells beneath the skin; glucose does not come directly from a blood vessel.

What is biofouling in CGM sensors?

Deposition of proteins and other substances on sensor surfaces leading to reduced accuracy.

What is the purpose of trend alerts in CGM (e.g., high/low alerts)?

Warn the patient of oncoming hyperglycemia or hypoglycemia and prompt action to avoid or mitigate events.

Where are CGM readings derived from in terms of sampling site?

From interstitial fluid via a skin-implanted sensor, not direct blood sampling.

What is the function of the transmitter in a CGM system?

Sends glucose data from the sensor to the reader/monitor.